U.S. patent application number 12/001879 was filed with the patent office on 2008-06-19 for process for the preparation of toluenediamines by catalytic hydrogenation of dinitrotoluenes.
This patent application is currently assigned to Bayer MaterialScience AG. Invention is credited to Wolfgang Lorenz, Lars Padeken, Bernd Pennemann, Fritz Pohl, Friedhelm Steffens, Gerhard Wiechers.
Application Number | 20080146847 12/001879 |
Document ID | / |
Family ID | 39226948 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080146847 |
Kind Code |
A1 |
Pohl; Fritz ; et
al. |
June 19, 2008 |
Process for the preparation of toluenediamines by catalytic
hydrogenation of dinitrotoluenes
Abstract
The present invention relates to a process for the preparation
of toluenediamine, in which dinitrotoluene is reacted with hydrogen
in the presence of a catalyst. The dinitrotoluene required by this
process has a content of carbon dioxide, in either physically
dissolved or chemically bonded form, of not more than 0.175 mol %,
based on the molar amount of the dinitrotoluene.
Inventors: |
Pohl; Fritz; (Brunsbuttel,
DE) ; Lorenz; Wolfgang; (Dormagen, DE) ;
Padeken; Lars; (Dusseldorf, DE) ; Pennemann;
Bernd; (Bergisch Gladbach, DE) ; Steffens;
Friedhelm; (Leverkusen, DE) ; Wiechers; Gerhard;
(Leverkusen, DE) |
Correspondence
Address: |
BAYER MATERIAL SCIENCE LLC
100 BAYER ROAD
PITTSBURGH
PA
15205
US
|
Assignee: |
Bayer MaterialScience AG
|
Family ID: |
39226948 |
Appl. No.: |
12/001879 |
Filed: |
December 13, 2007 |
Current U.S.
Class: |
564/419 ;
564/420; 564/422 |
Current CPC
Class: |
C07C 209/36 20130101;
C07C 209/36 20130101; C07C 211/50 20130101 |
Class at
Publication: |
564/419 ;
564/420; 564/422 |
International
Class: |
C07C 209/36 20060101
C07C209/36 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 19, 2006 |
DE |
102006060572.1 |
Claims
1. A process for the preparation of toluenediamine comprising
reacting dinitrotoluene with hydrogen in the presence of a
catalyst, wherein said dinitrotoluene has a content of carbon
dioxide in physically dissolved form or chemically bonded form of
less than 0.175 mol %, based on the molar amount of
dinitrotoluene.
2. A process for the preparation of toluenediamine, comprising: a)
reacting toluene with nitrating acid to form a reaction mixture
comprising mononitrotoluenes, b) separating said reaction mixture
comprising mononitrotoluenes into an organic phase comprising
mononitrotoluenes and an aqueous phase comprising sulfuric acid, c)
reacting said the organic phase comprising mononitrotoluenes with
nitrating acid, to yield a reaction mixture comprising an isomeric
mixture of dinitrotoluenes, d) separating said reaction mixture
comprising an isomeric mixture of dinitrotoluenes into an organic
phase comprising dinitrotoluenes and an aqueous phase comprising
sulfuric acid, e) purifying said organic phase comprising
dinitrotoluenes with water, in a multi-stage extraction in which
each stage comprises mixing and phase separation, to yield an
isomeric mixture of dinitrotoluenes comprising (i) from 74 to 81%
by weight of 2,4-dinitrotoluene, (ii) from 17 to 21% by weight of
2,6-dinitrotoluene, and (iii) less than 5.5% by weight of the
2,3-isomer, the 2,5-isomer, the 3,4-isomer and the 3,5-isomer of
dinitrotoluene, with the sum of (i), (ii) and (iii) totalling 100%
by weight of dinitrotoluene, f) reacting said isomeric mixture of
dinitrotoluenes with hydrogen, in the presence of a catalyst to
form toluenediamines, wherein (1) the dwell time for the mixing in
each stage of the multi-stage extraction in step e) is at least 4
minutes and not more than 60 minutes, and (2) an inert gas is
additionally introduced into the mixture of the organic phase
comprising dinitrotoluenes and water in at least the last stage of
the extraction in step e), with the weight ratio of inert gas to
dinitrotoluenes being such that the resultant purified isomeric
mixture of dinitrotoluenes have a total content of carbon dioxide
in physically dissolved or chemically bonded form of less than
0.175 mol %, based on the molar amount of the dinitrotoluenes.
3. The process of claim 2, wherein in e) said purifying step,
alkaline water is present in at least one stage of the multi-stage
extraction and neutral water is present in at least one stage of
the multi-stage extraction.
4. The process of claim 1, wherein said catalyst comprises at least
one nickel-containing catalyst.
5. The process of claim 2, wherein said catalyst comprises at least
one nickel-containing catalyst.
Description
CROSS REFERENCE TO RELATED PATENT APPLICATION
[0001] The present patent application claims the right of priority
under 35 U.S.C. .sctn. 119 (a)-(d) of German Patent Application No.
10 2006 060 572.1, filed Dec. 19, 2006.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a process for the
preparation of toluenediamine (TDA), in which dinitrotoluene (DNT)
is reacted with hydrogen in the presence of a catalyst, wherein the
dinitrotoluene used has a content of carbon dioxide in physically
dissolved or chemically bonded form of not more than 0.175 mol %,
based on the molar amount of the dinitrotoluene used.
[0003] Toluenediamines are intermediates for the preparation of
toluene diisocyanates (TDI), which are important preliminary
products, produced on a large scale, for the preparation of
polyurethanes. Their preparation by catalytic hydrogenation of
dinitrotoluenes (DNT) is known and has often been described (see,
for example, Ullmann's Enzyklopadie der technischen Chemie, 4th
Edition, Volume 7, page 393 ff, 1973, Verlag Chemie Weinheim/New
York). The industrial production of toluenediamines is carried out
predominantly by reaction of a mixture of isomeric dinitrotoluenes
that is obtainable by nitration of toluene with nitric acid.
Commercial mixtures of isomeric dinitrotoluenes are produced
predominantly in the form of crude DNT in a two-stage isothermal
nitration process using nitric acid in the presence of sulfuric
acid as catalyst, with the formation of the corresponding
mononitrotoluenes as intermediates. They are subsequently worked up
in stages provided downstream of the reaction, predominantly in
washing stages, and thus largely freed of dissolved sulfuric acid
and nitric acid, and also of secondary components such as, for
example, cresols and their degradation products, formed in the
reaction stages.
[0004] Typical commercial DNT products have DNT contents >98.5%
by weight, less than 0.1% by weight of mononitrotoluene, less than
0.1% by weight of trinitrotoluene and less than 0.1% by weight of
other secondary components, as well as small residual amounts of
toluene, based on the total weight of the DNT product mixture, with
DNT yields of >98% and toluene conversions of >99.9%. Also
important is the weight ratio of the total amount of the 2,4- and
2,6-DNT isomers to the total amount of the 2,3-, 3,4-, 2,5- and
3,5-DNT isomers. According to commercial specifications, the total
content of 2,4- and 2,6-DNT isomers in the crude DNT is >95% by
weight, based on the total weight of the crude DNT. The content of
2,4-DNT is preferably from 79.0% to 81.0% by weight, based on the
sum of the weights of 2,4-DNT and 2,6-DNT. Accordingly, the content
of 2,6-DNT is from 19.0% to 21.0% by weight, based on the sum of
the weights of 2,4-DNT and 2,6-DNT.
[0005] The catalytic hydrogenation of these commercial DNT products
can be carried out with the concomitant use of an inert solvent or
without a solvent, the mixtures then being melted before the
hydrogenation is carried out. It can be carried out either
discontinuously or continuously using conventional reactors. In
addition to a continuous reaction procedure, the selectivities of
the reaction that can be achieved with the process being used, and
the capacities and working lives of the catalysts used, are
especially important to the economic success of the process that is
used.
[0006] U.S. Pat. No. 3,356,728 discloses an improved continuous
process for the preparation of aromatic amines by catalytic
hydrogenation of aromatic polynitro aromatic compounds in a sludge
phase reactor, in which the process is explained using the example
of the reaction of dinitrotoluene. According to the teaching of
U.S. Pat. No. 3,356,728, the catalytic hydrogenation of
dinitrotoluene in this reaction system is carried out very
effectively in terms of selectivity, catalyst working life and
throughput if [0007] the reaction zone is always saturated with
hydrogen during the reaction, [0008] the aromatic polynitro
compound is added to the system while maintaining a specific weight
ratio to the catalyst present in the reaction system (i.e.
"catalyst loading"), [0009] and [0010] the concentration of the
added aromatic polynitro compound in the reaction zone does not
exceed a given limiting value.
[0011] U.S. Pat. No. 3,356,728 claims a working range <0.15, and
preferably a working range from 0.01 to 0.11, for the so-called
catalyst loading (i.e. "ratio of the added amount of aromatic
polynitro compound in kg equivalents of nitro groups per hour to
the catalyst present in the reactor in kg"). It also discloses that
the maximum concentration of aromatic nitro compound to be
maintained in the reaction mixture is 0.1% by weight, and
preferably less than 0.015% by weight, based on the weight of the
reaction mixture.
[0012] According to the teaching of U.S. Pat. No. 3,356,728, the
claimed catalyst loadings lead to high concentrations of active
catalyst in the reaction system, such that the aromatic polynitro
compound which is fed in is immediately reacted to the desired
amine after entering the mixture, and the concentration of
unreduced nitro compound in the reaction system is thereby kept
below 0.005% by weight at all times. As disclosed in U.S. Pat. No.
3,356,728, this low concentration prevents the catalyst from
rapidly being poisoned and, in addition, higher yields and improved
product purity are obtained at substantially reduced costs in the
reaction of the aromatic polynitro compound.
[0013] The avoidance of inadmissibly high concentrations of
unreduced nitro compound in the reaction mixture of catalytic
hydrogenations of aromatic polynitro compounds is also the
subject-matter of U.S. Pat. No. 3,499,034. U.S. Pat. No. 3,499,034
discloses 0.5% by weight, based on the weight of the reaction
mixture, as the maximum concentration of unreduced aromatic nitro
compounds that is to be maintained. According to the teaching of
U.S. Pat. No. 3,499,034, these low concentrations of unreduced
nitro compound especially bring about low concentrations of the
azoxy, azo and hydrazo compounds which, as is known, are also
formed in the catalytic hydrogenation of nitro compounds and which,
as described in U.S. Pat. No. 3,499,034, constitute tar-like
compounds, which can be reduced but only with difficulty and only
with a marked slowing down of the desired catalytic hydrogenation
of the aromatic polynitro compound.
[0014] According to the teaching of EP 0 171 052 B1, the formation
of tar-like intermediates in the catalytic hydrogenation of
aromatic nitro compounds is dependent not only on the concentration
of unreduced nitro compound but also on the nitro compound itself.
As disclosed in EP 0 171 052 B1, the catalytic hydrogenation of
aromatic nitro compounds is particularly successful if mixtures of
at least 25% by weight of mononitro-nonamino aromatic compounds
with at least 25% by weight of dinitro- or mononitro-amino aromatic
compounds are used as the aromatic nitro compounds. The advantage
of the disclosed reaction procedure is limited, however, in view of
the outlay that it is subsequently necessary to separate the
hydrogenation products by distillation. Thus, the catalytic
hydrogenation of aromatic polynitro compounds on a large scale is
conventionally carried out in accordance with the principles
outlined by way of example in U.S. Pat. No. 3,356,728 and U.S. Pat.
No. 3,499,034.
[0015] According to the teaching of GB Patent 832,153, the desired
catalytic hydrogenation of the nitro compound can be greatly
affected not only by the unreduced aromatic nitro compound and its
intermediate azoxy, azo and hydrazo compounds, but also by
contaminants contained in the nitro compound to be hydrogenated. As
disclosed in GB Patent 832,153, nitrophenols and nitrocresols,
which are usually present in small amounts in commercial
dinitrotoluene isomeric mixtures, are decomposition accelerators as
well as strong catalyst poisons, so their concentration is to be
regarded as critical in respect of process safety and in respect of
the efficiency of the desired catalytic hydrogenation of the nitro
compound to the corresponding amine. According to the teaching of
GB Patent 832,153, the nitro compound used in the catalytic
hydrogenation should contain less than 500 ppm "nitrophenols",
preferably less than 20 ppm "nitrophenols", with the term
"nitrophenols" being understood according to GB Patent 832,153 as
the sum of nitrophenol- and nitrocresol-like compounds.
[0016] EP 0 019 454 B1 also deals with the influence of
nitrophenol-like contaminants. According to the teaching of EP 0
019 454 B1, the removal of the nitrophenol-like contaminants is
largely unnecessary, but it is important in the catalytic
hydrogenation of commercial dinitrotoluenes, in order to avoid
catalyst poisoning and the decomposition of the amine that is
formed, to lower their acid content, expressed as HNO3, to below
6000 ppm, based on the weight of the dinitrotoluene. EP 0 019 454
B1 discloses a process in which the crude dinitrotoluene is washed
only with water; aqueous alkaline solutions are not used for
removing nitrophenol-like contaminants.
[0017] The statements made in U.S. Pat. No. 4,482,769 are more
differentiated. According to the teaching therein, washing of
commercial dinitrotoluene mixtures with aqueous alkaline solutions
is advantageous, but the washing should be carried out in such a
manner that the aqueous phase has a pH value in the range from 5.8
to 6.4. As disclosed in U.S. Pat. No. 4,482,769, the result of such
a pH value in the washing is that all the acidic components are
largely removed from the dinitrotoluene, with only
2,4-dinitroorthocresol, which is poorly biodegradable, remaining in
the dinitrotoluene as a secondary component. According to the
teaching of U.S. Pat. No. 4,482,769, on the one hand the influence
of acidic components is advantageously prevented by the claimed
process, and on the other hand a low content of
2,4-dinitroorthocresol does not affect subsequent hydrogenations of
the dinitrotoluene so prepared.
[0018] Surprisingly, it has now been found that in the preparation
of toluenedianine, in which dinitrotoluene is reacted with hydrogen
in the presence of a catalyst, the desired reaction is
substantially influenced not only by the parameters known according
to the prior art, but also by the carbon dioxide content of the
dinitrotoluene used in the reaction. More specifically,
substantially better catalyst working lives are obtained, while the
selectivity of the reaction is increased, if the carbon dioxide
contents of the dinitrotoluene are low.
SUMMARY OF THE INVENTION
[0019] The present invention provides a process for the preparation
of toluenediamine, in which dinitrotoluene is reacted with hydrogen
in the presence of a catalyst, characterised in that the
dinitrotoluene used has a content of carbon dioxide in physically
dissolved or chemically bonded form of less than 0.175 mol %, based
on the molar amount of the dinitrotoluene used.
[0020] A suitable analytical method to determine the content of
carbon dioxide in physically dissolved or chemically bonded form,
which can be used within the scope of the process according to the
invention, is disclosed and described in detail in the "Examples"
section below, under the title "Description of the analytical
method for the quantitative determination of carbon dioxide in
physically dissolved or chemically bonded form in dinitrotoluene".
Within the scope of this invention, the content of carbon dioxide
in physically dissolved or chemically bonded form is to be
understood as meaning the total content of carbon dioxide, which
can be present in physically dissolved and/or chemically bonded
form.
[0021] In a preferred embodiment of the invention, the process for
the preparation of toluenediamine comprises: [0022] a) reacting
toluene with nitrating acid to form a reaction mixture containing
mononitrotoluenes, [0023] b) separating the reaction mixture
containing mononitrotoluenes into an organic phase containing
mononitrotoluenes and an aqueous phase containing sulfuric acid,
[0024] c) reacting the organic phase containing mononitrotoluenes
with nitrating acid, to yield a reaction mixture containing
dinitrotoluenes (i.e. an isomeric mixture of dinitrotoluenes)
[0025] d) separating the reaction mixture containing
dinitrotoluenes into an organic phase containing dinitrotoluenes
and an aqueous phase containing sulfuric acid, [0026] e) purifying
the organic phase containing dinitrotoluenes with water in a
multi-stage extraction in which each stage comprises mixing and
phase separation, to yield an isomeric mixture of dinitrotoluenes
which contains (i) from 74% to 81% by weight of 2,4-DNT, (ii) from
17% to 21% by weight of 2,6-DNT, and (iii) less that 5.5% by weight
of 2,3-DNT, 2,5-DNT, 3,4-DNT and 3,5-DNT combined, with the sum of
(i), (ii) and (iii) totalling 100% by weight of dinitrotoluene,
[0027] f) reacting the resultant isomeric mixture of
dinitrotoluenes with hydrogen in the presence of a catalyst to form
toluenediamines, wherein [0028] (1) the dwell time (residence time)
for the mixing in each stage of the multi-stage extraction in step
e) is at least 4 minutes and not more than 60 minutes, and [0029]
(2) an inert gas is additionally introduced into the mixture of the
organic phase containing dinitrotoluenes and water in at least the
last stage of the extraction in step e), with the weight ratio of
inert gas to dinitrotoluenes being such that the resultant purified
dinitrotoluenes have a total content of carbon dioxide in
physically dissolved or chemically bonded form of less than 0.175
mol %, preferably of less than 0.125 mol %, and most preferably of
less than 0.075 mol %, based on the molar amount of the
dinitrotoluenes.
DETAILED DESCRIPTION OF THE INVENTION
[0030] In the process according to the invention, and in particular
in its preferred embodiment (i.e. steps a) to g) as described
above), the reaction in the preparation of the mononitrotoluenes in
step a) and of the dinitrotoluenes in step c) can be carried out
either adiabatically or isothermally. It is preferably carried out
isothermally using cooled stirrer vessel cascades through which the
reaction mixture flows continuously or series-connected cooled loop
reactors, such as are described in, for example, EP 0 903 336 B1,
which is believed to correspond to U.S. Pat. No. 5,902,910, the
disclosure of which is hereby incorporated by reference, or DE10
2004 005 913 A1. Static and dynamic separators can be used in the
phase separation as in steps b) and d). Preference is given to the
use of static separators as are described in, for example, in EP 0
903 336 B1, which is believed to correspond to U.S. Pat. No.
5,902,910, the disclosure of which is hereby incorporated by
reference.
[0031] In the preferred process of the invention, the multi-stage
extraction in step e) of the organic phase obtained in step d) can
be carried out with recovery of the principal amount of the nitric
acid and/or sulfuric acid contained in the organic phase. The
recovery can be carried out by a single- or multi-stage procedure
using small amounts of uncharged water in the individual stages, or
by a multi-stage procedure, counter-currently, using larger amounts
of water which are circulated through each stage. Suitable
processes are described in, for example, EP 0 279 312 B1 or EP 0
736 514 B1, which are believed to correspond to U.S. Pat. Nos.
5,001,286 and 5,756,867, respectively, and the disclosures of which
are hereby incorporated by reference.
[0032] There is preferably no recovery of acid. Then, in the
preferred process according to the invention, the
dinitrotoluene-containing organic phase obtained in step d) is
washed in step e) with water in a multi-stage extraction that
comprises mixing and phase separation in each stage. In a
particularly preferred embodiment, the water used for the
multi-stage extraction of the dinitrotoluenes (i.e. the isomeric
mixture of dinitrotoluene) can have different pH values in the
different stages. It is then preferred in step e) for the
extraction of the dinitrotoluenes to use alkaline water in at least
one stage and neutral water in at least one stage. In the case of
an extraction comprising more than two stages, it is preferred to
use alkaline water in at least one stage, acidic water in at least
one stage and neutral water in at least one stage. In this
preferred embodiment, the extraction in the stages is carried out
as a "liquid/liquid" extraction. This is ensured by suitably
choosing the temperatures of the dinitrotoluenes used and of the
aqueous phases used as the extraction agents.
[0033] In a further preferred embodiment, the multi-stage
extraction is carried out in at least one stage using an apparatus
for mixing and separating liquids of different specific gravities
that are virtually insoluble in one another, as is described in,
for example, DE-B-1 135 425, which is believed to correspond to
U.S. Pat. No. 3,162,510, the disclosure of which is hereby
incorporated by reference.
[0034] Characteristic features of the apparatus described in DE-B-1
135 425, which is believed to correspond to U.S. Pat. No.
3,162,510, the disclosure of which is hereby incorporated by
reference, are a mixing zone in the form of an extraction or
washing column, having a chamber for phase separation arranged
concentrically around the mixing zone, the mixture that leaves the
mixing zone entering the chamber via an overflow with a surrounding
hollow jacket of the "cut-off" washing column and being separated
into two phases on the basis of density. In order to allow the
apparatus described in DE-B-1 135 425 (which is believed to
correspond to U.S. Pat. No. 3,162,510, the disclosure of which is
hereby incorporated by reference) in column 2/lines 35-52 and
column 3/lines 1-12 in respect of its structure and in column
3/lines 29-47, in respect of its function to be used advantageously
in the process according to the invention, a possibility for the
supply of inert gas into the mixing zone, for example through an
additional opening in the region of the bottom of that portion of
the apparatus, should additionally be provided in the
apparatus.
[0035] It is, however, possible in principle to use for the
extraction in the purification step e), any form of multi-stage
extraction process and extraction apparatus comprising mixing and
phase separation in each stage, provided that the dwell time or
residence time for the mixing (i.e. the time period during which
the mixture is performed) in each stage of the extraction within
step e) is at least 4 minutes and not more than 60 minutes (see
requirement (1) in the preferred process above); and that an inert
gas is additionally introduced into the mixture of the organic
phase containing dinitrotoluenes and water in at least in the last
stage of the extraction within step e) (see requirement (2) in the
preferred process above). The weight ratio of inert gas to
dinitrotoluenes is such that the resultant purified dinitrotoluenes
have a total content of carbon dioxide in physically dissolved or
chemically bonded form of less than 0.175 mol %, based on the molar
amount of the dinitrotoluenes.
[0036] The required amount or the required weight ratio of inert
gas to the dinitrotoluenes can readily be determined by the person
of ordinary skill in the art. This amount or ratio is readily
determined by simple experimentation, by carrying out tests with
increasing amounts or weight ratios of inert gas to dinitrotoluenes
until the required content of carbon dioxide in physically
dissolved or chemically bonded form is reached.
[0037] The loading of the dinitrotoluene isomeric mixtures with
carbon dioxide in physically dissolved or chemically bonded form
that is achieved after the multi-stage extraction within the
purification step e) can preferably be monitored by gas
chromatography by means of "headspace GC". A suitable analytical
method for determining the content of carbon dioxide in physically
dissolved or chemically bonded form, which can preferably be used
within the scope of the process according to the invention, is
disclosed in the instant application in the section titled
"Description of the analytical method for the quantitative
determination of carbon dioxide in physically dissolved or
chemically bonded form in dinitrotoluene".
[0038] The dinitrotoluenes (dinitrotoluene isomeric mixture) so
prepared are preferably collected in a receiver and fed therefrom
in liquid form to the hydrogenation, which is preferably carried
out continuously. The dinitrotoluenes that preferably flow
continuously to the receiver can be subjected to a further
stripping gas treatment or a different type of carbon dioxide
removal either before they are collected in the receiver, after
they are in the receiver, or after they have been removed from the
receiver. The only important factor for the process according to
the invention is that the dinitrotoluene used in the catalytic
hydrogenation for the preparation of toluenediamine has a content
of carbon dioxide in physically dissolved or chemically bonded form
of less than 0.175 mol %, based on the molar amount of the
dinitrotoluene used.
[0039] The catalytic hydrogenation of the dinitrotoluene so
prepared can be carried out with the concomitant use of an inert
solvent or without a solvent. It is preferably carried out without
a solvent using an aqueous catalyst suspension. It can be carried
out either discontinuously or continuously using conventional
reactors. Examples thereof are stirrer vessels, bubble columns or
loop reactors, such as loop-Venturi reactors, or jet loop reactors
with an internal and external circuit.
[0040] In a preferred embodiment of the process according to the
invention, a jet loop reactor with an internal and external circuit
is used, as is described, for example, in EP 1 137 623 B1, which is
believed to correspond to U.S. Pat. No. 6,350,911, the disclosure
of which is hereby incorporated by reference.
[0041] In a further preferred form of the process according to the
invention, the catalytic hydrogenation of the dinitrotoluene having
a content of carbon dioxide in physically dissolved or chemically
bonded form of less than 0.175 mol %, based on the molar amount of
the dinitrotoluene used, is carried out in a sludge phase reactor
having an integrated heat exchanger such as is described in, for
example, WO-A-96/11052, which is believed to correspond to U.S.
Pat. No. 5,779,995, the disclosure of which is hereby incorporated
by reference. This reactor has, as the heat exchanger, an annular
chamber which is covered at the bottom and top by the reaction mass
in the reactor, the annular chamber having a plurality of vertical
flow channels for the reaction mass and the coolant flowing through
the annular chamber between the flow channels for the reaction
mass. As disclosed in WO-A-96/11052 which is believed to correspond
to U.S. Pat. No. 5,779,995, the disclosure of which is hereby
incorporated by reference, this reactor is particularly suitable
for dissipating the heat of reaction that is liberated during the
catalytic hydrogenation of the dinitrotoluene mixtures in the form
of usable steam. In the catalytic hydrogenation of the
dinitrotoluene according to the invention, an operating temperature
of from 80 to 200.degree. C., preferably from 100 to 180.degree.
C., and a pressure of from 5 to 100 bar, preferably from 10 to 50
bar, are maintained in the reactor.
[0042] The supply of hydrogen to the system is preferably carried
out in such a manner that the stoichiometric hydrogen requirement
for the reaction of the nitro group equivalents that are fed in to
the corresponding amine compounds is always covered and, in
addition, the contents of the reactor are always saturated with
hydrogen, taking particular account of the surface areas of the
catalyst(s) used. This is preferably achieved by providing the
sludge phase reactor that is preferably used with a gassing
stirrer, by means of which a largely homogeneous, fine distribution
of the catalyst(s) suspended in the reaction mixture and of the
hydrogen in the form of finely dispersed hydrogen bubbles in the
reaction mixture is produced.
[0043] According to the teaching of U.S. Published Patent
Application 2004/0073066 A1, it is advantageous to adjust the
purity of the hydrogen present in the reactor to from 50 to 97 vol
%, preferably from 70 to 97 vol %, and most preferably from 80 to
95 vol %, by the addition of inert compounds that are gaseous under
the hydrogenation conditions or by establishing an appropriate
purge gas stream for discharging the gaseous contaminants
introduced into the reactor with the hydrogen. According to the
teaching of U.S. Published Patent Application 2004/007366 A1, very
pure hydrogen has a strong tendency to coalesce in the reaction
system, with the result that the fine hydrogen bubbles combine
immediately downstream of the dispersion zone to form large bubbles
which have a small overall surface area. As disclosed in U.S.
Published Patent Application 2004/007366 A1, this coalescence does
not occur at relatively low hydrogen concentrations, the advantage
of a large surface area being eliminated at too low a hydrogen
concentration by too low a mass transfer.
[0044] In a particularly preferred form of the process, a sludge
phase reactor is used whose gassing stirrer is present in the form
of an axial conveyor, and in particular for gas/liquid dispersions,
as described in, for example, EP 0 856 665 B1, which is believed to
correspond to U.S. Pat. No. 6,627,174, the disclosure of which is
hereby incorporated by reference. By the particular choice of this
mixing member, one achieves, on the one hand, a very high
circulating capacity of the liquid phase, and on the other hand,
the desired distribution of the hydrogen in the form of finely
divided hydrogen bubbles in the reaction mixture is obtained in a
simple manner.
[0045] As described above, local overconcentrations are to be
avoided when metering the dinitrotoluenes into the reactor for the
catalytic hydrogenation. Metering can be carried out via lances,
nozzles or mechanically driven mixing devices. In a preferred form
it is carried out via a stirring device as described in, for
example, EP 1 637 220 A1, which is believed to correspond to U.S.
Published Patent Application 2006/0038306, the disclosure of which
is hereby incorporated by reference. This stirring device consists
at least of a gassing stirrer and a blade mixer or two liquid
mixers, which are arranged on a shaft and each have a feed and at
least one exit opening, the exit openings of the gassing stirrer
and of the liquid mixer or liquid mixers being at a defined
distance from one another. In the stirring device, the ratio "a/d"
of the distance "a" between the exit openings to the diameter "d"
of the gassing stirrer or liquid mixer ranges from 0.025 to 0.5,
preferably from 0.05 to 0.3, and the ratio "b/d" of the distance
"b" between the outside edges to the diameter "d" of the gassing
stirrer or liquid mixer ranges from 0.01 to 0.4, preferably from
0.02 to 0.2. The described stirring device is particularly suitable
for simultaneously mixing gas and liquid phases into a reaction
mixture, with optimised mixing of the phases avoiding local
overconcentrations of introduced nitro group equivalents to a
particular degree.
[0046] As catalysts there can be used any hydrogenation catalysts
which are known to be suitable for the catalytic hydrogenation of
aromatic nitro compounds. Particularly suitable are the metals of
sub-group 8 of the periodic system of the elements or mixtures
thereof, which can be applied, for example, to support materials
such as carbon or oxides of magnesium, aluminium and/or silicon.
Preference is given to the catalysts include, for example, Raney
iron, cobalt and/or nickel, and in particular nickel-containing
catalysts such as, for example, Raney nickel catalysts, as well as
palladium- or platinum-containing catalysts on support materials.
The preparation and use of such catalysts as hydrogenation
catalysts of aromatic nitro compounds such as, for example,
nitrobenzene, nitrotoluenes, dinitrotoluenes, chlorinated nitro
aromatic compounds and others, is known and has already been
described often. See, for example, EP 0 223 035 B1, EP 1 066 111 B1
and EP-A-1 512 459, which are believed to correspond to U.S. Pat.
No. 4,792,626, U.S. Pat. No. 6,395,934 and U.S. Published Patent
Application 2005/0107251, respectively, the disclosures of which
are hereby incorporated by reference.
[0047] In a most particularly preferred embodiment of the process
according to the invention there are used as catalysts the Raney
nickel catalysts such as those which are described in, for example,
EP-A-1 512 459, which is believed to correspond to U.S. Published
Patent Application 2005/0107251, the disclosure of which is hereby
incorporated by reference. As disclosed therein, the preparation of
these preferred catalyst comprises [0048] 1) the melt of an alloy
of from 50 to 95 wt. % aluminium, from 10 to 50 wt. % nickel, from
0 to 20 wt. % iron, from 0 to 15 wt. % cerium, cerium mixed metal,
vanadium, niobium, tantalum, chromium, molybdenum or manganese and
optionally also further glass-forming elements, is cooled with a
cooling rate >10.sup.4 K/s by pressing the molten alloy onto a
rotating cooling wheel or into the gap between two cooling wheels
rotating in opposite directions or by melt extraction, and [0049]
2) the rapidly solidified alloy is then subjected to treatment with
organic or inorganic bases.
[0050] In comparison to conventional Raney nickel catalysts, these
preferred catalysts are distinguished by a markedly increased
product selectivity and catalyst working life, and particularly at
reaction temperatures >120.degree. C. Consequently, when they
are used, the heat of reaction that is liberated in the
hydrogenation of dinitrotoluenes can advantageously be used to
produce steam for use as a heating medium.
[0051] The reaction mixture is removed from the reaction system,
which is preferably operated continuously, for the catalytic
hydrogenation of dinitrotoluenes according to the feeds, preferably
continuously while retaining the catalyst in the system. The
removal is particularly preferably carried out using cross-flow
filtration, as is described in principle in, for example, EP 0 634
391 B1, which is believed to correspond to U.S. Pat. No. 5,563,296,
the disclosure of which is hereby incorporated by reference, or in
a specific embodiment in EP 1 137 623 B 1, which is believed to
correspond to U.S. Pat. No. 6,350,911, the disclosure of which is
hereby incorporated by reference. In the case of this product
discharge, a partial stream is removed from the reactor and passed
over a cross-flow filter, where a partial amount is removed from
the product stream while the catalyst is retained, and finally the
reduced partial stream "concentrated" in respect of its catalyst
content is fed back to the reactor again.
[0052] The filtered product has high purity and can be processed
without further chemical after-treatment to form the end product
toluenediamine as described in the prior art.
[0053] In total, the process according to the invention for the
preparation of toluenediamine, in which dinitrotoluene is reacted
with hydrogen in the presence of at least one catalyst, is
distinguished by greatly improved economy as compared with to the
prior art processes. By the use of dinitrotoluene having a content
of carbon dioxide in physically dissolved or chemically bonded form
of less than 0.175 mol %, based on the molar amount of the
dinitrotoluene used, increased catalyst selectivities and
substantially improved catalyst working lives are obtained.
[0054] The process according to the invention is described in
greater detail hereinbelow by means of preferred embodiments.
[0055] The following examples further illustrate details for the
process of this invention. The invention, which is set forth in the
foregoing disclosure, is not to be limited either in spirit or
scope by these examples. Those skilled in the art will readily
understand that known variations of the conditions of the following
procedures can be used. Unless otherwise noted, all temperatures
are degrees Celsius and all percentages are percentages by
weight.
EXAMPLES
Description of the Analytical Method for the Quantitative
Determination of Carbon Dioxide in Physically Dissolved or
Chemically Bonded Form in Dinitrotoluene
[0056] For the quantitative determination of physically dissolved
or chemically bonded carbon dioxide in dinitrotoluene (DNT), a
defined DNT sample amount is placed in a rolled-edge glass jar that
can be sealed in a gas-tight manner by means of a septum, a defined
amount of sulfuric acid is added, and then the amount carbon
dioxide present in the gas chamber is determined by means of
headspace gas chromatography (i.e. headspace analysis by means of
gas chromatography) with thermal conductivity detection with
calibration by an external standard.
The Following Devices are Used in the Analytical Method:
[0057] HP 5890 gas chromatograph with thermal conductivity detector
(Hewlett-Packard)
[0058] HP 19 395A headspace sampler (Hewlett-Packard)
Separation Conditions:
[0059] stationary phase: silica gel #12, packed column (10
ft.times.1/8 in) carrier gas: helium (flow rate of 12.5 ml/min)
column oven, temperature: 200.degree. C. injection block,
temperature: 200.degree. C. detector, temperature: 250.degree. C.
headspace cell: 45.degree. C. incubation time: 3.0 min injection
volume: 1 ml
Completion of Quantitative Analysis:
[0060] For the analysis, 1.0 g.+-.0.1 mg of the DNT sample were
weighed into a rolled-edge glass jar. After the glass jar was
sealed, 0.50 ml of sulfuric acid (w=0.330 g/kg) were injected
through the septum by means of a syringe, the contents of the
rolled-edge glass jar were mixed by gentle shaking, and then the
rolled-edge glass jar was placed in the headspace sampler and,
after tempering, analysed by means of headspace GC.
[0061] The quantitative evaluation was carried out by means of an
external standard. Analogously to the analysis of the DNT sample, a
defined amount of aqueous sodium hydrogen carbonate solution having
a content w=0.5 g of NaHCO.sub.3/kg of solution was placed in a
vessel, sulfuric acid was added, and analysis was carried out by
gas chromatography.
Example 1
Hydrogenation of Dinitrotoluene Having a Content of Physically
Dissolved or Chemically Bonded Carbon Dioxide of 0.19 Mol % (not in
Accordance with the Invention)
[0062] The laboratory hydrogenation apparatus can be operated
continuously. The hydrogenation apparatus consisted of: [0063] a
heated amount of DNT covered with a layer of nitrogen, [0064] a DNT
metering pump with heated feed and discharge lines, [0065] a
one-liter hydrogenation reactor equipped with a heating/cooling
jacket, an internal cooling coil and a connected heating/cooling
system, a gassing stirrer, immersed metering lances and a fine-pore
frit having a connected discharge line, and [0066] a heated
separator for phase separation with pressure maintenance, level
measurement and heated discharge line for product removal, 800 g of
a mixture containing 62% by weigh of toluenediamine and 38% by
weight of water, based on 100% by weight of the mixture, were
introduced, with a covering of nitrogen, into the reactor, which
was preheated to 50.degree. C., and then a suspension of 50 g of
water and 7 g of a water-moist Raney nickel/iron catalyst having an
iron content of 15% by weight, based on the weight of the starting
alloy, was added. The closed apparatus was pressurised to 30 bar
absolute with hydrogen having a purity of >99.9 vol %, and the
reactor was heated to 140.degree. C., while operating the gassing
stirrer, and the desired temperature was maintained for 2 hours in
order to activate the catalyst, and the atmosphere of the
hydrogenation apparatus, in the pressure-bearing region, was freed
of the introduced inert compounds at a purge rate of 30 standard
liters/h.
[0067] 125 g/h of dinitrotoluene, which was stored in the receiver
at 75.degree. C., with a content of carbon dioxide in physically
dissolved or chemically bonded form of 0.19 mol %, was metered into
the apparatus prepared as described above. The pressure in the
system was maintained by maintaining the purge rate of 30 standard
liters/h by feeding in hydrogen having a purity of >99.9 vol %,
with the level in the reactor maintained at the desired level by
the frit, and the discharged, catalyst-free reaction mixture was
collected in the downstream separator and removed periodically
therefrom to take samples.
[0068] The quality of the reaction was monitored by high-pressure
liquid chromatography. After an operating time of 76 hours,
complete conversion was no longer observed. At this point, the
chromatograms indicated the breakthrough of nitro-amino aromatic
compounds, and the test was terminated.
Example 2
Hydrogenation of Dinitrotoluene Having a Content of Physically
Dissolved or Chemically Bonded Carbon Dioxide of 0.045 Mol %
(According to the Invention)
[0069] The test was prepared and carried out analogously as
described above in Example 1. However, a dinitrotoluene having a
content of physically dissolved or chemically bonded carbon dioxide
of 0.045 mol % was used.
[0070] The quality of the reaction was monitored by high-pressure
liquid chromatography. Only after an operating time of 162 hours
was complete conversion no longer observed, as illustrated by the
chromatograms which showed the breakthrough of nitro-amino aromatic
compounds. Thus, the test was terminated at that time.
Example 3
Hydrogenation of Dinitrotoluene Having a Content of Physically
Dissolved or Chemically Bonded Carbon Dioxide of 0.18 Mol % (not in
Accordance with the Invention)
[0071] Into a stirrer vessel that was rendered inert with nitrogen,
was continuously fed 5860 kg/h of a catalyst suspension that
contained 704 kg/h (about 12% by weight, based on the weight of the
suspension) of a Raney nickel/iron catalyst having an iron content
of about 30% by weight, based on the weight of the catalyst, and
27.1% by weight of m-TDA, 0.9% by weight of o-TDA, 37% by weight of
isopropanol, 23% by weight of water, with the %'s by weight being
based in each case on the total weight of the suspension. This was
mixed continuously in the mixing vessel with 5876 kg of a
commercial dinitrotoluene containing 99.4% by weight of
dinitrotoluene, based on the weight of the mixture, in which the
content of carbon dioxide in either physically dissolved or
chemically bonded form of 0.18 mol %, based on the amount of
dinitrotoluene used, and 5870 kg of prepared solvent containing 87%
by weight of isopropanol and 13% by weight of water, based on the
total weight of the prepared solvent, with the operating
temperature of the mixing vessel being maintained at 75.degree.
C.
[0072] The mixture as prepared above, was removed continuously from
the mixing vessel and fed to a high-pressure hydrogenation
installation, where it was reacted with hydrogen at 150.degree. C.
and 100 bar in a cooled reactor cascade that was operated in series
with respect to the circulated hydrogen and in parallel with
respect to the dinitrotoluene mixture used. The reaction mixture
left the reactor cascade after a mean dwell time of 21 minutes and
was cooled to 75.degree. C., and then fed to a phase separator,
where it was separated into a gas phase and a liquid phase.
[0073] The gas phase was fed back to the start of the reactor
cascade, and the hydrogen content of the gas phase was maintained
at concentrations >90 vol % by a purge stream. The liquid phase
was removed continuously from the separator and relieved into a
stirred filtration receiver, from which it was fed to a filtration
unit. In the filtration unit, the mixture was separated in such a
manner that, in addition to a clear filtrate, a catalyst suspension
that contained 12% by weight. of Raney nickel/iron catalyst, 27.1%
by weight of m-TDA, 0.9% by weight of o-TDA, 37% by weight of
isopropanol and 23% by weight of water was obtained. The clear
filtrate that was separated off was processed by distillation, and
the catalyst suspension produced was fed back to the mixing
vessel.
[0074] The catalytic activity of the circulated catalyst was
monitored by gas chromatography, and the ageing behavior of the
catalyst used was taken into account by the continuous supply of a
defined amount of fresh catalyst in the form of a 1% by weight of
suspension in water added to the mixing vessel, and the desired
concentration of the catalyst in the reaction chamber was
maintained by the periodic discharge of the catalyst suspension
produced in the filtration unit. The amount of fresh catalyst
required to maintain the catalytic activity, based on the amount of
toluenediamine prepared, was referred to as the specific catalyst
consumption.
[0075] When using dinitrotoluene having a content of carbon dioxide
in physically dissolved or chemically bonded form of 0.18 mol %,
based on the amount of dinitrotoluene, a specific catalyst
consumption of 27 g/100 kg of TDA was achieved.
Example 4
Hydrogenation of Dinitrotoluene Having a Content of Physically
Dissolved or Chemically Bonded Carbon Dioxide of 0.045 Mol %
(According to the Invention)
[0076] This example was carried out analogously as described above
in Example 3. However, a dinitrotoluene having a content of
physically dissolved or chemically bonded carbon dioxide of 0.045
mol % was used.
[0077] When using dinitrotoluene having a content of carbon dioxide
in physically dissolved or chemically bonded form of 0.046 mol %,
based on the amount of dinitrotoluene, a specific catalyst
consumption of 6 g/100 kg of TDA was achieved.
[0078] Although the invention has been described in detail in the
foregoing for the purpose of illustration, it is to be understood
that such detail is solely for that purpose and that variations can
be made therein by those skilled in the art without departing from
the spirit and scope of the invention except as it may be limited
by the claims.
* * * * *